A common type of irrigation sprinkler used to water turf and landscaping is referred to as a rotor-type sprinkler. It typically includes a riser that telescopes from an outer casing. The riser encloses a turbine that rotates a nozzle turret at the top of the riser through a reduction gear train and reversing mechanism. Typically the nozzle turret oscillates back and forth through an arc whose size can be adjusted depending on the area of coverage required. Vandals frequently twist the nozzle turret of rotor-type sprinklers which causes them to spray water outside their intended arc of coverage, often onto roads and sidewalks. When a vandal twists the nozzle turret of a rotor-type sprinkler to “back drive” the sprinkler, i.e. rotate the nozzle turret in a direction opposite the direction it is currently being driven by its turbine, strong rotational forces are transmitted to the reversing mechanism and reduction gear train, frequently damaging the same.
Rotor-type sprinklers often include some form of clutch that slips when the nozzle turret is rotated by an external force, i.e. one not generated by the turbine. A clutch in a rotor-type sprinkler must be able to transmit a steady rotational drive force to the nozzle turret so that the turbine can rotate the nozzle turret back and forth between the pre-set arc limits, or in some cases, rotate the nozzle turret continuously through three hundred and sixty degrees. However the clutch must be capable of breaking loose or disengaging when the nozzle turret is twisted by a vandal.
Rotor-type sprinklers have also been developed that include an automatic arc return mechanism so that the nozzle turret can be twisted out of arc by a vandal, and will resume oscillation within the intended arc of coverage without any resulting damage to the reduction gear train or reversing mechanism. See for example U.S. Pat. No. 6,050,502 granted to Clark on Apr. 18, 2000 and U.S. Pat. No. 6,840,460 granted to Clark on Jan. 11, 2005, both assigned to Hunter Industries, Inc., the assignee of the subject application.
Clutches and automatic arc return mechanisms that have heretofore been developed for rotor-type sprinklers have been too complex, required too many parts and/or been too unreliable. They have also not been suitable for retrofitting, i.e. installation into existing rotor-type sprinklers not originally designed with clutches to prevent back driving.